# Heat conductivity depending on temperature

Hi, I'm working on my final year project for a part time mechanical engineering design degree course. I've built and tested a heat exchanger which is used for controlling the temperature of N2 gas.

I'm currently working through the calculations so I can compare real against calculated values.

I'm struggling to calculate the thermal conductivity of N2 depending on temperature. An Engineer from work gave me a Visual basic file which had the following expression which works really well. The problem is I can't work out what the components are - and I'm not happy using it if I don't understand what it's doing

Visual basic expression.

Function lambda_N2 (Temp As Double)

' Calculation of heat conductivity (W/(m*K)) depending on temperature
' for gaseous N2 - source Malkov

lambda_N2 = 0
lambda_N2 = -0.000000054111 * Temp * Temp + 0.000102445 * Temp - 0.00016339

End Function

I assume that the values he's used are constants - but as yet I've been unable to trace them. Could someone explain what some or all of it is doing?

Or is there another way of calculating thermal conductivity?
(Note. I want it for an individual temperature not for ∆T)

Many thanks in advance
Oli

## Answers and Replies

Mapes
Science Advisor
Homework Helper
Gold Member
Hi Oli, welcome to PF.

The equation looks like an empirical fit to experimentally measured results (and as such, has little meaning without a temperature and pressure range). The constants are likely selected just to make the resulting curve fit well to measured values.

A much more involved equation with physical justification is given http://www.boulder.nist.gov/div838/theory/refprop/NAO.PDF" [Broken], which may be what you're looking for. The document also includes many references to experimental work, which may be useful.

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